1. Field of the Invention
The present invention relates to a polarizer for use in optical instruments utilizing the polarization phenomenon that is a property of the light, the polarizer permitting only the linearly polarized wave in a direction orthogonal thereto.
2. Description of the Related Art
Polarizer is an element which transmits only the light component which vibrates to a specific direction among the non-polarized light or elliptically polarized light whose electric 10- and magnetic field vibrates to non-specific directions to give the linearly polarized light. It is one of the most fundamental optical elements, and is widely used as a device for the optical communication, a pick-up for the optical disc, a liquid crystal display, optics-applying measurements, and so on. Operation modes of it can be roughly grouped into the following two modes: 1) the mode in which unnecessary polarized waves are absorbed, and 2) the mode in which two orthogonalized and polarized wave components which are emitted through the same light path are separated into different light paths. Depending on the purpose of utilizing a polarizer, the polarizer is required to have large aperture area, high performance, and so on or to be thin. It is industrially important to be able to supply such a polarizer inexpensively.
Presently a polarizer is generally practically used which was prepared by doping a polymer film with a dichromic molecule such as iodine in the case of operation mode 1. Although this type of polarizer can be obtained inexpensively and in a large area, its extinction ratio and its temperature stability are low, i.e., it has these faults.
In order to solve those problems, a polarizer prepared with materials having high stability has been developed, i.e., a polarizer prepared by arranging to one direction an absorber such as metal and semiconductor in a transparent body such as glass in minute lines or thin films. Polarized wave components which are parallel to the minute lines or thin films are absorbed or reflected, and polarized waves which are orthogonal to them are transmitted. Although this type of polarizer can have a high extinction ration, steps such as cutting and polishing might be necessary, i.e., it is difficult to reduce the production cost. In addition, it is difficult to produce a thin polarizer which has a large area.
On the other hand, a polarizer which is prepared with double refraction single crystals for operation mode 2 is prepared by sticking two triangular prisms which are made of a material which has a large double refraction coefficient such as calcite. A typical one is made of Gran Thomson prisms. Although this type of polarizer can have generally a high extinction coefficient and transmittance, it is difficult to produce a polarizer which has a large area or a thin one. The material is expensive, therefore the cost is high.
Polarizers utilizing the Brewster angle of a transparent body include a polarized beam splitter using a multilayer dielectric. Although it is inexpensive because it can be easily mass-produced, it has at least the following problems: high polarization is not obtained; miniaturization is difficult; and the wavelength band for use is narrow. Therefore, it is used only for limited purposes.
Each of the above-mentioned polarizers is practically used. On the other hand, very recently, a polarizer is theoretically proposed which utilizes an anisotropy of propagation property of a transparent body regularly arranged structure which has a pitch of the wavelength or shorter (Tetsuko Hamano, Masayuki Izutsu, and Hideki Hirayama, “Possibility of Polarizer Using Two-dimension Photonic Crystal,” 58th Applied Physics Autumn Proceedings, paper 2a-W-7, 1977; Akira Sato and Masahiro Takebe “Optically Anisotropic Multilayered Film by Structural Double Refraction,” Optics Japan '97 Proceedings, paper 30pD01, 1997). These polarizers have the structure in which thin pillars of a transparent body which has a refractive index which is different from the matrix are arranged two-dimensionally and regularly in a transparent matrix. If the structure satisfies a condition that the pitch is, for example, half-wave length or so, among polarized waves which are parallel and vertical to those pillars, one can be transmitted, and the other can be blocked, i.e., it can work as a polarizer. Actually, however, any method for industrially constructing such structure has not been found, and any experimental example has not been reported.
The present invention was conceived to solve the above-mentioned problems. The object of the present invention is to provide a polarizer which has an excellent extinction ratio and insertion loss property and has a large aperture area in spite of a small optical path length, and allows inexpensive industrial production.